The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Electronics present a safety hazard in environments where unintentional exposure to conductive liquids by dripping, spilling, submersion and condensation are possible. Ground fault detection provides protection from electric shock. Other failure mechanisms can produce smoke, arcing and other unintentional behavior that might otherwise go undetected. Sealed enclosures are in an option in some cases where cost and thermal performance are not critical factors. Cooling holes improve heat transfer but make waterproofing requirements difficult to meet.
Printed circuit boards (PCBs) are easily damaged by conductive liquids. Some have attempted to solve this problem by indiscriminately applying a hydrophobic coating to the PCB, but imperfections in the coating can lead to short circuit related hazards and damage, especially if the liquid is present for a long time as it eventually finds its way to exposed conductors.
Detection mechanisms for liquids have also been used. Liquids are often detected by resistive measurement between two electrodes. In its simplest form, such a detection element has two conductors side by side. When a conductive liquid is poured on top of the conductors, current can now flow between them. Detection circuitry picks up a change in voltage or current and some action is taken. For example, U.S. Pat. No. 4,297,686 discusses this technique, shutting off water in the event of pipe leaks to prevent flooding. This and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
A very simple example of detection circuitry 100 is depicted in FIG. 1A, which illustrates a circuit with two conductive plates that serves as detection artwork. The term “artwork” is used here because the plates could be easily implemented as circles of exposed copper on an outer layer of a circuit card. A comparator in this example handles the detection. When a conductive liquid shorts the plates as shown in FIG. 1B, the comparator signals an alert by illuminating a light-emitting diode (LED).
Capacitive means have also been used to detect liquids. In a most basic form, such a mechanism utilizes two conductors spaced by a dielectric such as air or the substrate to which they are mounted. The conductors need not be exposed but will have a capacitance between them. As liquid approaches or contacts the sensing conductors, the dielectric properties between, and therefore capacitance between, the conductors is altered. This can then be detected by measuring circuitry and signal an action to be taken.
While these technologies each pose a potential solution to the problem of sensing liquids, they fail to address the need for the detectors to be exposed to the liquid before damage to other components may occur. In this manner, by the time the liquid is detected, damage may already have occurred.
Thus, there is still a need in the art for improved conductive liquid protection for PCBs.